Fullerenes are closed-cage molecules composed entirely of sp2 hybridized carbons, arranged in hexagons and pentagons. Fullerenes (e.g. C60) were first identified as closed spheroidal cages produced by condensation from vaporized carbon.
Fullerene tubes are produced in carbon deposits on the cathode in carbon arc methods of producing spheroidal fullerenes from vaporized carbon. Such tubes are referred to herein as carbon nanotubes. Many of the carbon nanotubes made by these processes are multi-wall nanotubes i.e. the carbon nanotubes resemble concentric cylinders. Carbon nanotubes of seven walls have been described in the prior art.
Single-wall carbon nanotubes (SWNT) have been made in a DC arc discharge apparatus of the type used in fullerene production by simultaneously evaporating carbon and a small percentage of VIII B transition metal from the anode of the arc discharge apparatus. It is also known that the use of mixtures of such transition metals can significantly enhance the yield of single-wall carbon nanotubes in the arc discharge apparatus. While the arc discharge process can produce single-wall nanotubes, the yield of nanotubes is low and the tubes exhibit significant variations in structure and size between individual tubes in the mixture. Individual carbon nanotubes are difficult to separate from the other reaction products and purify.
A method of producing single-wall nanotubes is described in U.S. Pat. No. 6,183,714 entitled “Ropes of Single-Walled Carbon Nanotubes” incorporated herein by reference in its entirety. This method uses, inter alia, laser vaporization of a graphite substrate doped with transition metal atoms, preferably nickel, cobalt, or a mixture thereof, to produce single-wall carbon nanotubes in yields of at least 50% of the condensed carbon. The single-wall nanotubes produced by this method tend to be formed in clusters, termed “ropes,” of 10 to 1000 single-wall carbon nanotubes in parallel alignment, held together by van deer Waals forces in a closely packed triangular lattice. Nanotubes produced by this method vary in structure, although one structure tends to predominate.
A method of producing carbon fibers from single-wall carbon nanotubes is described in PCT Patent Application No. PCT/US98/04513, incorporated herein by reference in its entirety. The carbon fibers are produced using molecules in a substantially two-dimensional array made up of single-walled nanotubes aggregated (e.g., by van deer Waals forces) in substantially parallel orientation to form a monolayer extending in directions substantially perpendicular to the orientation of the individual nanotubes. In this process the seed array tubes are opened at the top (free) end and a catalyst cluster is deposited at this free end. A gaseous carbon source is then provided to grow the nanotube assembly into a fiber. In various processes involving metal cluster catalysis, it is important to provide the proper number of metal atoms to give the optimum size cluster for single wall nanotube formation.
Since the discovery of single wall carbon nanotubes (SWNTs) in 1993 researchers have been searching for ways to manipulate them chemically. While there have been many reports and review articles on the production and physical properties of carbon nanotubes, reports on chemical manipulation of nanotubes have been slow to emerge. There have been reports of functionalizing nanotube ends with carboxylic groups and then further manipulation to tether them to gold particles via thiol linkages Haddon and co-workers have reported solvating SWNTs by adding octadecylamine groups on the ends of the tubes and then adding dichlorocarbenes to the nanotube side wall, albeit in relatively low quantities. While theoretical results have suggested that functionalization of the nanotube side-wall is possible, chemical modification of nanotube surfaces via covalent and ionic interactions to improve their solubility modify the chemical integrity of the carbon nanotube.
PCT Publication No. WO 00/17101, which is hereby incorporated by reference in its entirety describes the chemical derivization of single-wall carbon nanotubes to facilitate solvation and uses of the derivatized nanotubes. Chemical modification of the carbon nanotube structure would adversely affect both the mechanical and electrical properties of the carbon nanotubes. Another system reported in the literature utilizes a polymer wrapping technique.